1. Field of the Invention
The present invention relates to a fuel tank system of a motor bicycle wherein its tank main body is integrally molded out of a synthetic resin so as to freely form a shape of the tank, increase a capacity of the tank, and to facilitate a process of manufacturing the tank itself.
2. Description of the Related Art
For example, in the case where a fuel supply port of the aforesaid tank main body made of a synthetic resin is provided with a flat surface recessed type tank cap that is referred to as an aircraft type tank cap, there has been employed a structure in which the fuel supply port of the tank main body is provided with a metallic receiving pan portion, and a tank cap is fixed onto the receiving pan portion by means of a bolt.
While driving in rainy weather or during refueling, water or fuel may gather on the surface of the receiving pan portion. For this reason, there is a need for a drain pipe to discharge water or fuel from the surface of the receiving pan portion. Conventionally, a metallic pipe has been used as the drain pipe. The metallic pipe typically passes through so as to provide a connection between the receiving pan portion and a relay joint, which is provided in the tank main body itself. The relay joint is attached in an inconspicuous place such as the inside of a portion where the tank main body rides on a vehicle-body frame, and is also connected so that a hose extends to the outside therefrom.
However, tank main bodies that are made of a synthetic resin have a number of disadvantages. Specifically, when the tank main body swells due to contact with a fuel, it then becomes slightly deformed (e.g., mainly enlarged) in its whole dimensional shape. For this reason, there is a possibility that a spacial dimension between the receiving pan portion of the fuel supply port and the relay joint varies. In such a case, a metallic drain pipe having no expandability is not adaptable to a dimensional deformation between the receiving pan portion and the relay joint. Because the metallic drain pipe is not adaptable, an unreasonable force is applied to a connective section of the drain pipe. As a result, there is a possibility of causing deterioration in seal performance. Further, because the metallic drain pipe is not capable of being formed into a complicated or curved shape a drain discharge direction cannot be easily selected.
Moreover, if the tank main body is made of metal, then during assembling (e.g., a welding process) the drain pipe is simultaneously assembled into the interior of the tank main body. If the tank main body is made of a synthetic resin, however, the following process is required. After the tank main body is molded, a worker inserts a hand through the fuel supply port and into the interior of the tank main body to assemble the relay joint and the drain pipe therein. Then, the receiving pan portion is attached to the fuel supply port. As a result, assembling workability or performance of the tank main body is worsened depending upon where the relay joint is positioned.
As also described above, the tank main body swells due to contact with a fuel. For this reason, a fixed portion of the tank main body must be attached so as to be relatively movable with respect to the vehicle-body frame. This is so because the fixed portion must be floatingly fixed to the vehicle-body frame in order to achieve a vibration-proof tank main body.
To give a general example of a conventional fuel tank system, a front portion of the tank main body made of a synthetic resin has been provided with two right and left front portion fixing members while a rear portion thereof is provided with one rear portion fixing member. The front portion fixing member is formed like a plate that is parallel to a central surface of the vehicle body (i.e., in a longitudinal direction), and the front portion fixing member is fastened to the vehicle-body frame by means of a fixed bolt that penetrates along a vehicle width direction. On the other hand, the rear portion fixing member is formed like a substantially horizontal plate, and the rear portion fixing member is fastened to the vehicle-body frame by means of a fixed bolt that penetrates along a vertical (i.e., up and down) direction.
For example, a fixed bolt insertion hole of the rear portion fixing member is formed like a slot. Even if a dimension of the tank main body varies due to swelling, the rear portion fixing member is relatively slidable with respect to the fixed bolt so that a dimensional deformation of the tank main body can be absorbed. Further, rubber cushions or the like are interposed between three respective front and rear fixing members and the fixed bolt. As a result, vibration of the vehicle body may be prevented from being transmitted directly to the tank main body.
As described above, the front portion fixing member supporting the front portion of the tank main body has been formed like a plate that is parallel to the central surface of the vehicle body. For this reason, if the tank main body expands to a large scale size, then a high load acts along a direction of shearing the cushion rubber. Moreover, during rough road driving conditions or the like, a great push-up reactive force from a front fork may be applied to the tank main body via the front portion fixing member. Therefore, the rubber cushions may be crushed. As a result, it has been difficult to obtain a sufficient vibration-proof effect with respect to reactive forces in the vertical direction.
In addition, if the tank main body expands to a large scale size, then a dimensional deformation becomes large when the tank main body swells as a result of being spread in various directions. For this reason, even if only one of fixing members is fixed so as to be relatively movable with respect to the vehicle frame, it is impossible to absorb a dimensional deformation of the whole tank main body. For this reason, there is a high possibility that an unreasonable deformation stress is applied to the tank main body.
Further, there is a motor bicycle in which the tank main body made of a synthetic resin is covered with a frame cover made of a synthetic resin in order to protect the tank main body and to freely make a design having an attractive appearance. In this type of motor bicycle, if a structure is employed such that the frame cover is fixed directly to the tank main body, an unreasonable force may be applied to the frame cover due to a dimensional deformation, which may be caused by swelling of the tank main body. For this reason, the frame cover may become warped or damaged.
In view of the above circumstances, the following conventional fixing structure has been employed. Specifically, the frame cover is fixed to other members (e.g., vehicle-body frame or the like) positioned at the vicinity of the tank main body without being fixed directly to the tank main body. Or, only one portion of the frame cover is fixed to the tank main body, and other portions of the frame cover are fixed to the tank main body through the use of a surface fastener or the like so that a positioning correction can be easily made.
In the case where a relatively small tank main body is covered by a one-piece type frame cover, there is no problem even if the aforesaid fixing structure is employed. However, if the tank main body is enlarged to a large scale size, it is difficult to perform integral molding of the frame cover, and the frame cover must be constructed by being divided into a plurality of cover members and then joining these cover members together. For this reason, with the aforesaid fixing structure, a shift, unevenness or the like may occur between each of the plurality of cover members or between the cover members and the tank main body itself. As a result, the visible appearance around the fuel tank system may be remarkably deteriorated.
In a general fuel tank system of a motor bicycle, the tank main body has a shape of a reverse U-letter shaped longitudinal section (e.g., substantially the shape of a horseshoe), and is located so as to ride on the front head portion of the vehicle-body frame. Two or three fixing brackets provided on the front and rear portions of the tank main body are fixed and supported to the vehicle-body frame.
In particular, if the tank main body has a large capacity, a pair of right and left cushion members provided on the side of the vehicle-body frame are abutted against inner right and left longitudinal wall surfaces of a reverse U-letter shaped sectional portion of the tank main body. Accordingly, a great motion of the tank main body relative to a vehicle width direction is limited. In this manner, when a great force is applied to the side to the tank main body, such as due to a fall-down or collision of the motor bicycle, a stress to the fixing bracket is prevented from being concentrated and, thereby, damaged.
The attachment structure described above is effective in a tank main body that is made of metal. However, if the tank main body is integrally molded out of a synthetic resin material, then the tank main body can be swelled (e.g., expanded) by contact with a fuel. For this reason, elastic cushion members provided on the vehicle-body side may abut against the inner longitudinal wall surfaces. When the tank main body swells and deforms, the inner longitudinal wall surfaces are necessarily pressed against elastic cushion members. As a result, there is the possibility that a deformation is generated in the tank main body. Moreover, stress forces may also be concentrated on respective fixing brackets.
Further, regardless of the quality of the material of which the tank main body is made, in order to interpose the elastic cushion member between the vehicle-body frame and the inner longitudinal wall surface of the tank main body, a space between the vehicle-body frame and the tank main body must be made wide. For this reason, the capacity of the tank main body may need to be reduced.
By the way, in order to provide another independent component such as a tank cap or the like on the tank main body, the following method is employed. Specifically, when the tank main body is integrally molded out of a synthetic resin, a metallic insert nut is embedded, and the another independent component is fastened to the insert nut by means of a bolt. In the case of attaching the tank cap, a ring-like gasket (e.g., made of rubber) is interposed between the tank main body and the tank cap so that fuel leakage may be prevented.
However, the insert nut, which is embedded when the tank main body is integrally molded out of a synthetic resin, has a tendency such that the distal end surface is projected about 0.5 to 1.0 mm from the surface of the tank main body by hardening and shrinkage of the synthetic resin material after the tank main body is molded out of a synthetic resin. For this reason, for instance, in the case where the gasket is interposed between the tank main body and the tank cap so as to attach the tank cap as described above, the gasket bits into the projected distal end surface of the insert nut. As a result, seal performance remarkably deteriorates, and there is a possibility that the integrity of the gasket itself may be compromised.
Morever, without being limited to a single tank cap embodiment, in the case where other components made of a synthetic resin are fastened to the insert nut, there is the possibility that other types of soft components may be damaged by contact with the insert nut. Furthermore, various insert nuts may project or protrude unevenly. For this reason, it is difficult to stably fasten other components to all of insert nuts.